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use std::marker::PhantomData;

use crate::Node;

pub trait Lens: 'static + Sized {

    type Source: Node;
    type Target;

    fn view<'a>(&self, data: &'a Self::Source) -> Self::Target;
}


/// Helpers for manipulating `Lens`es
pub trait LensExt: Lens {

    /// Compose a `Lens<Source = A, Target = B>` with a `Lens<Source = B, Target = C>` to produce a `Lens<Source = A, Target = C>`
    fn then<Other>(self, other: Other) -> Then<Self, Other>
    where
        Other: Lens + Sized,
        Self: Sized,
    {
        Then::new(self, other)
    }

    fn and<Other>(self, other: Other) -> And<Self, Other>
    where
        Other: Lens + Sized,
        Self: Sized,
    {
        And::new(self, other)
    }

    fn index<I: 'static>(self, index: I) -> Then<Self, Index<Self::Target, I>>
    where
        Self: Sized,
        I: Clone,
        Self::Target: std::ops::Index<I> + Sized,
        <<Self as Lens>::Target as std::ops::Index<I>>::Output: Sized + Clone,
    {
        Then::new(self, Index::new(index))
    }
}

// Implement LensExt for all types which implement Lens
impl<T: Lens> LensExt for T {

}

/// `Lens` composed of two lenses joined together
#[derive(Debug, Copy)]
pub struct Then<A, B> {
    a: A,
    b: B,
}

impl<A, B> Then<A, B> {
    pub fn new(a: A, b: B) -> Self
    where
        A: Lens,
        B: Lens,
    {
        Self {
            a,
            b,
        }
    }
}

impl<A, B> Lens for Then<A, B>
where
    A: Lens,
    B: Lens<Source = A::Target>,
{

    type Source = A::Source;
    type Target = B::Target;

    fn view<'a>(&self, data: &'a Self::Source) -> Self::Target {
        self.b.view(&self.a.view(data))
    }
}

impl<T: Clone, U: Clone> Clone for Then<T, U> {
    fn clone(&self) -> Self {
        Self {
            a: self.a.clone(),
            b: self.b.clone(),
        }
    }
}

pub struct And<A,B> {
    a: A,
    b: B,
}

impl<A,B> And<A,B> {
    pub fn new(a: A, b: B) -> Self 
    where 
        A: Lens,
        B: Lens,
    {
        Self {
            a,
            b,
        }
    }
}

impl<A,B> Lens for And<A,B> 
where 
    A: Lens,
    B: Lens<Source = A::Source>,
{
    type Source = A::Source;
    type Target = (A::Target, B::Target);

    fn view<'a>(&self, data: &'a Self::Source) -> Self::Target {
        (self.a.view(data), self.b.view(data))
    }
}

pub struct Index<T,I> {
    index: I,
    output: PhantomData<T>,
}

impl<T,I> Index<T,I> {
    pub fn new(index: I) -> Self {
        Self {
            index,
            output: PhantomData::default(),
        }
    }
}

impl<T,I> Lens for Index<T,I> 
where 

    T: 'static + std::ops::Index<I> + Sized,
    I: 'static + Clone,
    <T as std::ops::Index<I>>::Output: Sized + Clone,
{
    type Source = T;
    type Target = <T as std::ops::Index<I>>::Output;

    fn view<'a>(&self, data: &'a Self::Source) -> Self::Target {
        data[self.index.clone()].clone()
    }
}